Amplifier circuit



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AMPLIFIER CIRCUIT' Filed oct, '20, 195s VVVW.

lNvENToRs KARL STEIMEL ATT RNEY Patented Jan. 17, 1939 UNITED STATES PATENT. OFFICE AllMLIFIER CIRCUIT Application October 20, 1933, Serial No. 694,375

2 Claims.

This invention relates to arrangements for the control of the amplication of amplifier circuits. More particularly it relates to arrangements for controlling the slope of the characteristic curve of amplifier circuits.

For the amplication of a controlled discharge system the steepness of the amplifier characteristic is of essential importance. In order to control the amplification, tubes have been constructed in which the steepness varies along' wide parts of the characteristic so that by displacing the working point the system operates with varied steepness. Such so-called exponential tubes are often provided in amplifier arrangements in which the sensitivity can be controlled. A disadvantage of such arrangements resides in the fact that due to the operation upon the curved characteristic, distortions occur in the output circuit. If the amplication is intended to be varied without the occurrence of distortion, an arrangement must be used which operates upon a linear characteristic and in which the steepness of this characteristic is adjustable while its linearity is safeguarded. Such arrangements are described by the invention.

The accompanying drawing illustrates diagrammatically a circuit arrangement embodying the invention. In said drawing two tubes 4I and d are connected in parallel; the tube il is a screen grid tube and is provided with an input circuit connected between the signal grid and the cathode thereof. The anode is connected through an ouput load or impedance to the positive terminal of a source of uni-directional current, the negative terminal of which is connected to the cathode. The screen grid of tube l is connected to the positive terminal of the source through an unbypassed resistor R. Tube 4@ is shown as a triode and is arranged so that the anode thereof is connected to the screen grid end or" the resistor R, whereas the cathode of the triode is connected to the negative terminal of the source and the grid is connected to the cathode of tube t0 through a source of control voltage.

From a study of the drawing, it will be seen that the current through the resistor R is divided into two paths, one path being through the tube 4@ to the grid of which the control voltage is applied and the other path being through the screen grid circuit of the amplifying tube M. The characteristic of tube 4l is changed by changing the controlled voltage applied to tube 4B. The potential of the screen grid of tube 4I is obtained :from the source Germany November 5, 1932 of unidirectional current through the resistor R. One path from the positive terminal of the source is through R, the connection to the screen grid and thence through the space charge path of the tube to the cathode and through the lower lead to the negative terminal of the source. This path is in part shunted by a Vshunt path extending from the upper terminal of resistor R through the space discharge path of tube 40 to its cathode which is likewise connected to the negative terminal of the source. The control voltage may be applied to the grid of tube 40 to vary its space current. Thus the impedance of the shunt path including the space current path of tube 40 may be varied and in this way the current flowing between the screen grid and cathode of tube lil can be varied, thus changing the screen grid'potential and thereby controlling the steepness of the tube characteristic.

It will be seen that in the arrangement shown in the drawing the screen current in tube il is also controlled by the control grid potential of tube il and decreases as the control grid potential becomes more negative. This causes an vincrease of screen potential due to the lessened voltage drop in the screen circuit resistance. Thus, the application of an alternating voltage to the control grid results in an opposite phased voltage appearing upon the screen grid. If it were not for the unbypassed resistance in the screen circuit of tube lll no alternating voltage would appear upon the screen. Therefore, the provision of unbypassed resistance R in the screen circuit of tube 4|, in effect, constitutes a means for insuring or, in other words, impressing an alternating voltage of opposite phase upon the screen.

What we claim is:

l. In combination in an amplifying system, a screen grid amplifying tube having an anode, an input circuit'for said tube, an output circuit for said tube including said anode and a source of positive potential, a second vacuum tube having a cathode, a control grid and an anode,'an unbypassed resistor and said source of Vpotential connected between said cathode and anode of said second vacuum tube, a conductive connection between said anode and the screen grid of said first tube and means for applying a control voltage to the control grid of said second tube whereby to vary the slope of the amplification characteristic of said screen grid tube.

2. In a system of the class described, the combination of a rst vacuum tube having a cathode, a first control electrode, a second control electube and the other end of said resistor, a source of potential having its positive terminal connected to the last named end of said resistor and its negative terminal connected to the cathodes of said tubes and means for applying a 5 control voltage tothe grid of said second tube.

KARL STEIMEL. RUDOLF URTEL. 

